Acoustic-electric-energy converter



April 30, 1935. E L, ow Es 1,999,862

ACOUSTIC ELECTRIC ENERGY CONVERTER Filed Nov. 21, 1930 Patented Apr; 30, 1935 UNITED STATES ACOUS'IIC-ELECTRIC-ENERGY CONVERTER Edward Llndley Bowles, Wellesley Farms, Mass. I AppllcationNovember 21, 1930, Serial No. 497,166

I 19 Claims. The present inventiomthough havingfields of more general usefulness, is more particularly related to devices for converting or translating acoustic into electric energy. d vice V l From amore limited aspect, the inventionrelates to diaphragms andxto loud speakers embodying the same. v p

' It has long been recognized, for theoretical reasons that need not be entered into here, that the ideal'coupling element in an acoustical system is not a diaphragm but rather a piston.

Transmitters or microphones, as commonly used at the present time in the communication 'art, employing metal membranes or di p 1 that are clamped along their peripheries, do not satisfy this ideal condition as the diaphragm does not move as a piston, being clamped along its periphery. In one such device, for example, a cup or button of carbon granules is held against I the face of the diaphragm. The vibration of the diaphragm causes variation in the resistance of the carbon particlesgand this, in turn, varies an electric current. Aside from the fact that the resistance variation is non-linear, the device introduces distortion due to the various modes of vibrationof the diaphragm, so that the transmission is not faithfully reproduced. The condenser transmitter, another common translating device, has a fixed conducting surface disposed exceedingly close and parallel to a metal diaphragm. Vibrations in the diaphragm cause variations in the distance and, therefore, the capacitance, between the two conducting elements, and the variations in capacitance is made use of to modulate a current, which may then be amplified. Here, again, the diaphragm intro duces new frequencies because-of its harmonic modesof vibration. .It has also been proposed to make the diaphragm in the shape of a funnel. or a frustum of a cone to move a large volume of air and to have a maximum of rigiditygwlth the driving coil at. the small end of the funnel, the diaphragm being freely suspended, at its larger end. This construction, though it does not require a rigid circumferential clamp, is still subject to the same theoretical defects. above mentioned and which make themselves felt, in practice. Other proposals, too, have been made, none of which has, however, proved to be successful.

. An Object of the present invention is to provide a very sensitive converter of energy of the abovedescribed character that shall translate, with greater fidelity than, is possible with present-day electro-dynamic methods, acoustic into electric energy or vice versa.

A further object is to provide a new and improved acoustic piston and a new and improved loud speaker embodying the same. This piston will, hereinafter, for convenience and by analogy, be referred to as a diaphragm.

Other objects will be explained hereinafter, and will be more particularly pointed out in the appended claims. I

The invention will be explained iniconnection with the accompanying drawing, in which Fig. 1 is a plan illustrating the present invention in its preferred form; Fig. 2 is a longitudinal section of the same, taken. upon the line 2-' 2 of Fig. 1, lookis] ing inthe direction of the arrows; Fig. 3 is a perspective of a preferred piston; and Fig. 4 is a plan and Fig. 5a a vertical section of amodification. 7

According to the present invention, the piston comprises. an evacuated vessel, made of metal or any other. suitable material. Duralumin and aluminum are good metals. The evacuation of the vessel may be effected in any desired way as, for example, by leaving a-small orifice in the vessel, inserting the vessel in a vacuum, under a Bell jar, and arranging a mechanical, vacuumlocked arrangement, so that, by means of an electric soldering iron, the orifice may beclosed when the Bell jar has been sufficiently evacuated. As 0 a further example of methods known to the art, a small tubulation could be secured to the vessel, which could then be evacuated through this very small tubulation. Once the evacuation process has been accomplished, the tubulation could be 5 squeezed, and held tight under pressure until soldered, so as .to become hermetically sealed.

The evacuated vessel is suspended by a series of radially disposed, comparatively light fibres or suspension strings 2 that are attached, at one 40 end, to the periphery of the membrane and, therefore, to the hereinafter mentioned moving coil I! also. The external atmospheric pressure acts to self-stretch the membrane, as distinguished from the kind of stretching that is imposed by 45.

some kind of clamping mechanism which exerts clamping forces along the periphery of the membrane, which literally gets hold of the metal and tends to pull it apart, thus stretching it in a different sense. This self-stretching of the vessel gives it rigidity and thus piston characteristics without the burden of weightwhich attends a structure made rigid by mechanical or structural means. Any small change in pressure on-the membrane in a given region due to themembrane being actuated by currents in the moving coil l2 will be so small compared to the total atmospheric pressure on that area that there will be no tendency for that area to move in relation to any other area in the membrane surface. The membrane will thus freely vibrate transversely of itself in reciprocative fashion, like a piston.

A preferred. form of vessel is a cylindrical body, shown in its original form by dotted lines in Fig. 2, the top and bottom faces 4 and 8 being caused to concave or bulge inward toward each other by atmospheric pressure. Though the faces 4 and 3 are thus bulged inward, the vessel is mechanically resistant to any tendency to flatten out entirely, being thus uncollapsible. Being placed under high tension by the atmospheric pressure on the faces a and G of the periphery 8, the membrane becomes very rigid and stiff, and moves as a rigid body. The term evacuated is used in the specification and the claims to include a partial, as well as a complete, vacuum, the purpose of the evacuation as before explained, being to cause the periphery 8 or" the cylinder to become very rigid and stiff, so as to resist efiectively the deforming forces that might otherwise be introduced by the movement of the diaphragm. Because of the rigidity and stillness thus attained, the element, when inserted in a sound field, will vibrate, piston-like, as a unit, thus reproducing, in facsimile, in an electric circuit, for example, waves of exactly the same wave shape as the shape of the waves of the sound field. In other words, the element will introduce no distortional harmonics or overtones due to additional modes of vibration of the element, because such additional modes of vibration are thus eliminated. The invention is not, however, limited to cylindrical diaphragms, as other shapes, also, will operate. In Fig. 4, for example, the diaphragm is illustrated as an evacuated sphere Id. In this case, of course, the sphere I0 is not stretched, in the ordinary sense of the term, but it is under high compression which makes it more rigid and less likely to be influenced by local sound pressure. The spherical shape is advantageous because it carries with it, in its movement, a large volume of air.

The evacuated diaphragm may be vibrated, substantially as a rigid body, in any well known way, as by means of an electromagnetic coil 2, to produce sound vibrations. The electromagnetic coil I 2 is, of course, secured rigidly to the periphery 8 of the evacuated vessel. Current may be led to and from the coil i2 through two of the supporting wires 2, by means of two separate, very flexible, leads 2% and 22- connected to the moving coil HE. A direct-current field structure is shown comprising a core it, with its gap, and its exciting or magnetizing coil M. Owing to the above-described structure, the motion of the diaphragm will approximate very closely to a true reciprocatory, or piston-type, drive. In addition to this advantage, there is no entrapped air to interfere with the operation, particularly if the degree of evacuation is high.

Further modifications will occur to persons skilled in the art, and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An acoustic-energy converter comprising a self-stretching, sealed evacuated vessel, and means for vibrating the vessel as a unit.

2. An acoustic-energy converter comprising a self-stretching, sealed, evacuated cylindrical vessel, and means for vibrating the vessel as a unit.

3. An acoustic-energy converter comprising a sealed, evacuated spherical vessel and means for vibrating the vessel.

4. An acoustic-energy converter comprising an evacuated vessel, shaped to produce stress in the walls thereof without collapsing in response to atmospheric pressure, and means for actuating the vessel like a piston.

5. Apparatus of the character described having, in combination, a self-stretching acousticenergy converter, and means for reciprocatively vibrating the converter as a unit.

6. Apparatus of the character described having, in combination, a pressure-stretched, acoustic-energy converter that is sufiiciently rigid to render it substantially free from overtones, means for suspending the converter so that it shall be capable of substantially transverse movement, and means for vibrating the converter transversely as a. unit.

'7. Apparatus of the character described having, in combination a pressure-stretched acoustic-energy converter sufiiciently rigid to render it substantially free from overtones, a. plurality of strings supporting the same so that it may vibrate reciprocatively, and means for reciprocatively vibrating the converter as a unit.

8. Apparatus of the character described having, in combination, an acoustic-energy converter comprising a self-stretching, sealed evacuated vessel, means for suspending the vessel so that it may vibrate like a piston, and means for reciprocatively vibrating the vessel as a unit.

9. Apparatus of the character described having, in combination, an acoustic-energy converter comprising a self-stretching, sealed evacuated vessel, means for suspending the vessel from points along its periphery so as to render it free to vibrate as a piston, and means for reciprocatively vibrating the vessel as a unit.

10. A loud speaker having, in combination, a radiating element comprising an evacuated vessel, means for suspending the element so that it shall be capable of substantially transverse movement as a unit, and means for vibrating the element transversely as a unit.

11. An acoustic-energy converter comprising a. sealed vessel, the pressure on the inside of the vessel being different from the pressure on the outside of the vessel, and means for vibrating the vessel as a unit.

12. An acoustic-energy converter comprising an evacuated vessel that is uncollapsible under atmospheric pressure, and means for vibrating the vessel as a unit.

13. An acoustic-energy converter comprising a self-stretching, sealed, evacuated vessel that is uncollapsible under atmospheric pressure, and means for vibrating the vessel as a unit.

14. An acoustic-energy converter comprising an evacuated cylindrical vessel that is uncollapsible under atmospheric pressure, and means for vibrating the vessel as a unit.

15. An acoustic-energy converter comprising a self-stretching, sealed, evacuated cylindrical vessel that is uncollapsible under atmospheric pressure, and means for vibrating the vessel as a unit.

16. An acoustic-energy converter comprising an evacuated spherical vessel that is uncollapsible under atmospheric pressure, and means for vibrating the vessel.

1,999,862 17. An acoustic-energy converter comprising a sealed, evacuated spherical vessel that is uncollapsible under atmospheric pressure, and means for vibrating the vessel.

18. Apparatus of the character described having, in combination, a pressure-stretched, acoustic-energy converter that is uncollapsible under atmospheric pressure, and means for reciprocatively vibrating the converter as a'unit.

19. Apparatus of the character described having, in combination, an acoustic-energy converter evacuated to render it substantially rigid and that is uncollapsible' under atmospheric pressure, means for suspending the converter so that it may vibrate as a piston, and means for reciprocatively vibrating the converter as a unit.

EDWARD LINDLEY BOWLES. 

